1. Field of the Invention
The present invention relates generally to the discovery and production of hydrocarbons, and more particularly, to the monitoring of downhole formation properties during drilling and production.
2. Background Art
Wells for the production of hydrocarbons such as oil and natural gas must be carefully monitored to prevent catastrophic mishaps that are not only potentially dangerous but also that have severe environmental impacts. In general, the control of the production of oil and gas wells includes many competing issues and interests including economic efficiency, recapture of investment, safety and environmental preservation.
On one hand, to drill and establish a working well at a drill site involves significant cost. Given that many xe2x80x9cdry holesxe2x80x9d are drilled, the wells that produce must pay for the exploration and digging costs for the dry holes and the producing wells. Accordingly, there is a strong desire to produce at a maximum rate to recoup investment costs.
On the other hand, the production of a producing well must be monitored and controlled to maximize the production over time. Production levels depend on reservoir formation characteristics such as pressure, porosity, permeability, temperature and physical layout of the reservoir and also the nature of the hydrocarbon (or other material) extracted from the formation. Additional characteristics of a producing formation must also be considered, such characteristics include the hydrocarbon/water interface, the hydrocarbon/gas interface and/or oil-water interface, among others.
Producing hydrocarbons too quickly from one well in a producing formation relative to other wells in the producing formation (of a single reservoir) may result in stranding hydrocarbons in the formation. For example, improper production may separate an oil pool into multiple portions. In such cases, additional wells must be drilled to produce the oil from the separate pools. Unfortunately, either legal restrictions or economic considerations may not allow another well to be dug thereby stranding the pool of oil and, economically wasting its potential for revenue.
Besides monitoring certain field and production parameters to prevent economic waste of an oilfield, an oilfield""s production efficiencies may be maximized by monitoring the production parameters of multiple wells for a given field. For example, if field pressure is dropping for one well in an oil field more quickly than for other wells, the production rate of that one well might be reduced. Alternatively, the production rate of the other wells might be increased. The manner of controlling production rates for different wells for one field is generally known. At issue, however, is obtaining the oil field parameters while the well is being formed and also while it is producing.
In general, control of production of oil wells is a significant concern in the petroleum industry due to the enormous expense involved. As drilling techniques become more sophisticated, monitoring and controlling production even from a specified zone or depth within a zone is an important part of modern production processes.
Consequently, sophisticated computerized controllers have been positioned at the surface of production wells for control of uphole and downhole devices such as motor valves and hydro-mechanical safety valves. Typically, microprocessor (localized) control systems are used to control production from the zones of a well. For example, these controllers are used to actuate sliding sleeves or packers by the transmission of a command from the surface to downhole electronics (e.g., microprocessor controllers) or even to electromechanical control devices placed downhole.
While it is recognized that producing wells will have increased production efficiencies and lower operating costs if surface computer based controllers or downhole microprocessor based controllers are used, their ability to control production from wells and from the zones served by multilateral wells is limited to the ability to obtain and to assimilate the oilfield parameters. For example, there is a great need for realtime oilfield parameters while an oil well is producing. Unfortunately, current systems for reliably providing realtime oilfield parameters during production are not readily available.
Moreover, many prior art systems may require a surface platform at each well for monitoring and controlling the production at a well. The associated equipment, however, is expensive. The combined costs of the equipment and the surface platform often discourage oil field producers from installing a system to monitor and control production properly. Additionally, current technologies often fail to reliably producing real time data. Often, production of a well must be interrupted so that a tool may be deployed into the well to take the desired measurements. Accordingly, the data obtained is expensive in that it has high opportunity costs because of the cessation of production. It also suffers from the fact that the data is not true realtime data.
Some prior art systems measure the electrical resistivity of the ground in a known manner to estimate the characteristics of the reservoir. Because the resistivity of hydrocarbons is higher than water, the measured resistivity in various locations can be of assistance in mapping out the reservoir. For example, the resistivity of hydrocarbons to water may be about 100 to 1 because the formation water contains salt and, generally, is much more conductive.
Systems that map out reservoir parameters by measuring resistivity of the reservoir for a given location are not always reliable, however, because they depend upon the assumption that any present water has a salinity level that renders it more conductive that the hydrocarbons. In those situations where the salinity of the water is low, systems that measure resistivity are not as reliable indicators of hydrocarbons.
Some prior art systems for measuring resistivity include placing an antenna within the ground for generating relatively high power signals that are transmitted through the formation to antennas at the earth surface. The amount of the received current serves to provide an indication of ground resistivity and therefore a suggestion of the formation characteristics in the path formed from the transmitting to the receiving antennas.
Other prior art systems include placing a sensor at the bottom of the well in which the sensor is electrically connected through cabling to equipment on the surface. For example, a pressure sensor may be placed within the well at the bottom to attempt to measure reservoir pressure. One shortfall of this approach, however, is that the sensor does not read reservoir pressure that is unaffected by drilling equipment and formations since the sensor is placed within the well itself.
Other prior art systems include hardwired sensors placed next to or within the well casing in an attempt to reduce the effect that the well equipment has on the reservoir pressure. While such systems perhaps provide better pressure information than those in which the sensor is placed within the well itself, they may not provide accurate pressure information that is unaffected by the well or its equipment.
Alternatives to the above systems include sensors deployed temporarily in a wireline tool system. In some prior art systems, a wireline tool is lowered to a specified location (depth), secured, and deploys a probe into engagement with the formation to obtain samples from which formation parameters may be estimated. One problem with using such wireline tools, however, is that drilling and/or production must be stopped while the wireline tool is deployed and while samples are being taken or while tests are being performed. While such wireline tools provide valuable information, significant expense results from xe2x80x9ctrippingxe2x80x9d the well, if during drilling, or stopping production.
Various techniques have been developed to obtain information concerning downhole conditions using sensors positioned about the well-bore. For example, PCT Application No. WO 02/06628 A1 published on Jan. 24, 2002 to Shultz et al. (priority based on U.S. patent application Ser. No. 09/617,212 filed on Jul. 17, 2000) discloses sensors placed in cement slurry about the well-bore and interrogating the sensors. U.S. Pat. No. 6,131,658 filed on Mar. 1, 1999 by Minear discloses sensors on an umbilical cable attached to tubing. Australian Patent Application No. 200027759 A1 published on Oct. 26, 2000 to Schultz et al. (priority based on U.S. patent application Ser. No. 09298725 filed Apr. 23, 1999) discloses sensor modules positioned within a formation or the well annulus and capable of sending signals to a well receiver.
Various techniques have also been developed for positioning plugs in casing. For example, U.S. Pat. No. 5,692,565 to MacDougall et al. discloses a device for plugging and resealing the perforation with a solid plug.
Despite these new techniques, there exists a need in the art for a well-bore system that efficiently senses downhole parameters and/or conditions so that decisions can be made concerning the drilling and production process so that such activities may be performed in a controlled manner that avoids waste of the hydrocarbon resources or other resources produced from it. It is further desirable for the system to be capable of deploying the sensors about the well-bore and/or plug perforations.
To overcome the shortcomings of the prior systems and their operations, the present invention contemplates a system for obtaining data from a subsurface formation penetrated by a well-bore. The system includes at least one sensor plug for sensing downhole parameters, the at least one sensor plug positionable adjacent the sidewall of a well-bore. The system also includes a downhole tool disposable in the well-bore, the downhole tool carrying the at least one sensor plug for deployment into the sidewall of the well-bore.
In some embodiments, the sensor plug is deployed in to the sidewall of an openhole well-bore. In other embodiments, the sensor plug is deployed into the sidewall of a cased well-bore. The downhole tool may optionally be utilized as a communication link between the sensor plug and the central control unit. Alternatively, an antenna may be positioned adjacent the well-bore to act as the communication link between the sensor plug and the central control unit. The downhole tool may also be equipped to perform a variety of downhole functions such as sampling, measuring and/or drilling operations.
Because the sensor plugs are already deployed, the downtime associated with gathering sensor plug information via a wireline tool is minimized. Because the invention may be implemented through MWD tool, there is no downtime associated with gathering sensor plug information during drilling. Accordingly, formation information may be obtained more efficiently, and more frequently thereby assisting in the efficient depletion of the reservoir.
In an embodiment of the described embodiment, a system for obtaining downhole data from a subsurface formation penetrated by a well-bore is provided. The system comprises a downhole tool disposable in the well-bore, the downhole tool carrying at least one sensor plug for deployment into the sidewall of the well-bore, a surface control unit and a communication link capable of operatively coupling the sensor plug to the surface control unit for communication therewith.
A central control center may be provided to communicate with a plurality of well control units deployed at each well for which sensor plugs have been deployed. Some wells include a drilling tool that is in communication with at least one sensor plug while other wells include a wireline tool that is communication with at least one sensor plug. Other wells include permanently installed downhole electronics and antennas for communicating with the sensor plugs. Each of the wells that have sensor plugs deployed therein include circuitry for receiving formation data received from the sensor plugs. In some embodiments, a well control unit serves to transpond the formation data to the central control unit. In other embodiments, an oilfield service vehicle includes transceiver circuitry for transmitting the formation data to the central control system. In an alternate embodiment, a surface unit, by way of example, a well control unit merely stores the formation data until the data is collected through a conventional method.
Some of the methods for producing the formation data to the central control center for analysis include conventional wireline links such as public switched telephone networks, computer data networks, cellular communication networks, satellite based cellular communication networks, and other radio based communication systems. Other methods include physical transportation of the formation data in a stored medium.
The central control center receives the formation data and analyzes the formation data for a plurality of wells to determine depletion rates for each of the wells so that the field may be depleted in an economic and efficient manner. In the preferred embodiment, the central control center generates control commands to the well control units. Responsive thereto, the well control units modify production according to the received control commands. Additionally, the well control units, wherever installed, continue to periodically produce formation data to the central control center so that local depletion rates may be modified if necessary.
The remote sensor plug is, in the preferred embodiment of the invention, is deployed into the sidewall of the well-bore. The internal circuitry of the sensor plug includes data acquisition circuitry, communication circuitry, control circuitry and a power supply. The data acquisition circuitry can include many different types of sensors that are commonly used to acquire formation data. For example, the data acquisition circuitry can include temperature sensors, pressure sensors, and resistivity sensors. The communication circuitry, in the preferred embodiment, includes demodulation circuitry for demodulating received control commands and modulation circuitry for modulating formation data. Additionally, the communication circuitry includes an RF oscillator for producing a carrier for the formation data. Finally, the power supply includes circuitry to convert received RF power to a direct current that is used to charge a capacitor or an energy charge component such as a rechargeable battery. The capacitor, in turn, is used to provide power for the operation of the sensor plug.
In another aspect, the present invention relates to a method for obtaining downhole data from a well-bore and its surrounding subterranean formation. The method comprises positioning a downhole tool in a well-bore, deploying at least one sensor plug from the downhole tool into the sidewall of the well-bore, collecting downhole data from the well-bore via the sensor plug and communicating the downhole data from the sensor plug uphole via a communication link. The downhole tool contains at least one sensor plug adapted for deployment.
In yet another aspect, the present invention relates to a method for controlling downhole operations from a surface control center. The method comprises positioning a downhole tool in a well-bore, deploying at least one sensor plug from the downhole tool into the sidewall of the well-bore, collecting downhole data from the well-bore via the at least one sensor plug, communicating the downhole data from the at least one sensor plug uphole to a surface control center via a communication link, making decisions based on the downhole data and communicating commands to a downhole tool via the communication link. The downhole tool contains at least one sensor plug adapted for deployment.
Other aspects of the present invention will become apparent with further reference to the drawings and specification that follow.